It's not madness at all, and people were not insane. The answer goes back to a book,The Care and Feeding of Children, first published in the 1890s by Dr. Luther Emmett Holt, which became the bible for child-rearing for decades. Dr. Holt prescribed "airing" of babies and children and keeping rooms very cool, sleeping with windows open unless it is below freezing. Airing the baby meant dressing her up and opening all the windows, even in winter, starting when the child was a month old. It sounds crazy, but here is an excerpt. His book is written as a Q and A: